1. Field of the Invention
The present invention relates to a positioning apparatus and, more particularly, to a multi-bar balanced parallelogram-type positioner.
2. Prior Art
The use of a kinematic linkage for positioning applications, such as five-bar and other types, is generally known in the art. One such linkage uses rotary motors to drive two main links of a five-bar linkage to provide two-degree-of-freedom planar positioning capability. In another such linkage, the pivots for the two main links are colinear, but the links are driven by rotary motors above and below the linkage resulting in asymmetry about the mid-line of the linkage and producing obstacles above and below the plane of motion.
However, nowhere in the prior art is there provided a combined linkage and actuator structure that is completely symmetric about the mid-plane to avoid out-of-plane reaction moments. Out-of-plane reaction moments can cause unwanted vibrations of the apparatus or the mounting structure and thus reduce operating performance In addition, none of the known prior art devices use limited angle rotary actuators as extensions of main links to provide a balanced structure with minimum inertia. In robotics, some attempts have been made to provide robots which are balanced against gravity to void the need for continuous actuator effort to counteract gravitational forces on the robot itself or its load. However, this balance has been obtained by adding large counterbalance masses to the robot structure or by using entire actuator assemblies as counterbalance elements, which can severely affect the dynamic performance. Although active torque cancellation devices are known and used to produce reactionless rotary actuators, such as in satellite applications, these cancellation devices have not been used to cancel the reaction moments of a planar positioning device.
It is therefore an objective of the present invention to provide a new improved positioning apparatus that can overcome problems in the prior art as well as provide additional features.